Dear Engineers; I had a headache from this problem : I run analysis in Etabs for a G+4 Project using Ritz so it runs okay. But I wished to convert some
columns to shell elements instead of frame elements then I run the etabs but the response spectrum
analysis could not start. when I look into "Last analysis Log..." I found the following :
" The strum sequence check found 5 eigen values below the shift
Ritz analysis requires All eigen values to be above the shift " Regards